Reference 320M amplifier was initially conceived as a larger, more powerful version of the Reference 160M amplifier, but it turned out to be a more complex combination of designs among the other Reference amplifiers. What was showcased in 2022 was a concept, not a product. The 330M is a very different beast, producing 330 watts of power per channel.

Reference 330M is unique, combining new thinking, new design, and new components with the best concepts from other Reference amplifiers. All gain is achieved using vacuum tubes; transistors are used only for impedance buffering.

The new front-end borrows the architecture of the 610T and uses ECC83 tubes for voltage gain. The ECC83 output is buffered using a special bipolar transistor with tube characteristics. The bipolar buffer allows us to maximize input stage margin and maintain the best sound quality of the ECC83.

The second stage is the classic circuit used in the 610T and 250, featuring a differential pair of 6H30 transistors biased by a DMOS current source. The 6H30 board is bootstrapping from the output stage.

To drive the output transistors, we use a new type of silicon carbide (SiC) JFET. These devices enable us to automatically bias each output transistor to the ideal quiescent current, and they also maximize driver margin and help us provide better bottom-end control

The output driver is also output-bootstrapping, providing more headroom during periods of large signal fluctuations.

The output transistors are the new KT170 model, which improves plate voltage margin, peak cathode current, and plate dissipation. They sound fantastic, with a strong musical quality. In a properly designed circuit, the KT170 delivers unparalleled high-level performance.

This power supply features solid-state regulation for the front end and tube regulation (6H30 and 6550) for the output tube display and driver stages. It also features a Pi filter using a large choke coil to reduce output stage power supply ripp

330M is a fully balanced amplifier from input to output. It operates using only pentodes because they provide the highest performance. Select the screen and board voltage for optimal linearity.

The rear panel includes balanced XLR and single-ended RCA inputs, 8Ω and 4Ω output taps, a 12V trigger, RS-232 control, a tube timer, 20A IEC, and fan speed adjustment.

Electronic Specifications

Output power: 330 watts

Tube bias
Automatic bias

Output taps: 4Ω, 8Ω

Tubes
(6) KT170 power output
(1) ECC83 & (1) 6H30 input
(1) 6550 & (1) 6H30 power supply

Input
XLR and single-ended

Control
12V trigger
RS-232 remote control

Power saving standby mode

Weight
101 lbs